Magnetic resonance angiography in a case of agenesis of the left carotid artery associated with transellar intercarotid anastomosis

Congenital absence or hypoplasia of the internal carotid artery is an extremely rare developmental abnormality. Usually these patients are asymptomatic because of functional compensation via the circle of Willis. A less frequent collateral circulation can occur by way of the primitive maxillary artery, an embrionic vessel originating from the controlateral carotid siphon and running through the sella turcica. We describe a fortuitous finding of unilateral agenesis of the internal carotid artery with intercavernous anastomosis in a patient with a meningioma adhering to the lateral margin of the right anterior clinoid. The case was studied by CT, MRI, MR angiography and digital subtraction angiography.